The present invention relates to processes which permit adherence between metal bodies and rubber, these metal bodies being in particular reinforcements used to reinforce rubber articles which may, for instance, be various manufactured articles such as tubes, plies, belts or tires, the metal reinforcements being, for instance, wires, assemblies of wires, or bead rings.
The invention also relates to the articles obtained by these processes.
The invention relates, very particularly, to the case in which the metal bodies are of stainless steel.
It is known to incorporate metal compounds, in particularly cobalt compounds, into rubber compositions in order to favor the adherence of the metal reinforcements to rubber. Such compounds are described, for instance, in French A-2 198 830, and U.S. Pat. No. 2,912,355.
This technique has the following drawbacks:
the metal compounds extensively modify the working properties and the performance of the vulcanized compositions, in particular the resistance to thermal and thermo-oxidizing aging is substantially altered; furthermore, the incorporating of these compounds in the compositions is costly and the metals of these compounds may at times be scarce; PA1 the adherence can, in general, be obtained only on copper, zinc, brass or bronze surfaces, so that it is necessary to effect a coating with these metals or alloys on the metal reinforcement when the latter is of a different constitution, for instance when it consists of steel, which is very commonly used for the reinforcements; such a metal coating is difficult to effect on stainless steel surfaces, since it is then generally necessary to apply a sub-coat, for instance of nickel, before effecting this coating; PA1 the adherence performances of the reinforcements obtained are at times insufficient and one can note, in particular, poor adhesion at high temperatures, degradation over the course of time and/or with respect to corrosion, in particular corrosion in the presence of water. PA1 a body is used at least the surface of which is of stainless steel, this steel containing at least 0.02% and at most 0.2% carbon, at least 3% and at most 20% nickel, at least 12% and at most 28% chromium, the sum of the nickel and chromium being at least equal to 20% and at most equal to 35%, all these percentage values being by weight; the structure of the steel comprises at least 20% by volume martensite and is without austenite or it comprises less than 80% thereof by volume; PA1 the surface of the body is activated and then treated with at least one starting silane so that it is covered with a film constituted only, or substantially only, of one or more silanes, in such a way that this surface treated in this manner can be placed directly in contact with the composition. PA1 I.sub.int =the integrated intensity of the peak PA1 L.sub.mh =the width at mid-height of the peak (in degrees) PA1 I.sub.max =the intensity of the peak (in counts per second) PA1 P=the measurement pitch of the peak (0.05 degrees). PA1 Gamma austenite: face centered cubic PA1 .alpha.' martensite: body centered cubic or body centered tetragonal PA1 .epsilon. martensite: hexagonal. PA1 I.sub.i =sum of the integrated intensities of all the peaks of said phase "i" PA1 I.sub.t =sum of the integrated intensities of all the peaks of all the diffraction phases of the steel. PA1 I.sub..alpha.' =integrated intensity of all the peaks of .alpha.' martensite PA1 I.sub..epsilon. =integrated intensity of all the peaks of .epsilon. martensite PA1 I.sub.gamma =integrated intensity of all the peaks of gamma austenite.
It is known to use coatings of brass formed by an electrolytic or chemical deposit of copper and zinc, this brass which has diffused well permitting a bonding to compositions which contain low concentrations of cobalt compound or which may even be without such compounds. These coatings have the drawback of being more difficult to produce than the aforesaid coatings and the bonding thus obtained is of poor resistance to thermal aging or thermo-oxidizing aging, for instance in the presence of water.
U.S. Pat. No. 4,441,946 and French A-2 320 974 describe a process for adhering steel to a rubber composition by applying a silane to the surface of the steel before placing it in contact with the composition. Stainless steels are not mentioned in those documents.